1. Field of the Invention
The present invention relates to a composition and a test strip for colorimetric analysis (detection and determination) of ascorbic acid present in an aqueous liquid, particularly, in body fluid.
The ascorbic acid (hereinafter, referred to as VC) is contained in foods, fodders and beverages, especially in enriched ones, and in nutritional supplement pills at relatively high concentrations. Thus, it is present in body tissues, blood and excrements at a correspondingly high concentration when they are ingested by or administered to humans or animals.
When detection or determination of another particular substance in the body fluid, especially urine or blood, is intended, there is a frequent possibility of creating an abnormal error in the measurement value of the other substance intended to be determined because of the high reducing ability of the coexistent VC which greatly affects the value.
For instance, when determination of the amount of glucose, galactose, cholesterol or uric acid in the body fluid is intended to be performed in accordance with a detection system composed of an enzyme, having an oxidizing activity specific to the particular substance, and peroxidase together with a redox chromogen, or when a detection of minute amounts of blood in urine is intended to be performed in accordance with a detection system of peroxidase and chromogen, a negative deviation from the actual amount may occur to an extent corresponding to the amount of the coexisting VC.
On the other hand, if determination of the amount of glucose, uric acid and the like is intended to be performed by a system based on a reduction method, a positive deviation from the actual value may occur to an extent corresponding to the amount of the coexistent VC.
2. Description of the Prior Art
Colorimetric titration analysis with indophenol is a heretofore widely known method for measuring VC in aqueous solutions. This method is, however, hardly regarded to be a practical method in clinical chemistry.
In clinical analysis, it is imperative to detect and determine the coexistent VC simultaneously with or, preferably, prior to the measurement of the previously mentioned other substances. The method for the latter measurement, which may be affected by the presence of VC, needs to be changed or modified according to the result of the determination of the coexistent VC.
Namely, it is desired to enable one to perform the detections and determinations of both substances in order to obtain accurate values thereof in an operation which is as simple as possible within a short period of time, thereby making the evaluation of the particular substance itself and its calibration with respect to the VC content possible at the same time.
One desired and simplified method for the measurement has been proposed in the specification of Japanese Patent Publication No. 712/78. This method is based on a principle that phosphorous molybdate can react with a substance having a reducing activity to form molybdenum blue (molybdenum oxide) and has been utilized as a known method for a quantitative determination of minute amount of inorganic phosphor. This method is, however, still unsatisfactory because the applicable range of VC concentration is limited only to 0-40 mg/dl and because of poor stability in the color development.